ORTHOGONAL SLIT CUT STACKED CIRCULAR PATCH MICROSTRIP ANTENNA FOR MULTIBAND OPERATIONS Surendra K. Gupta, 1 Ashish Sharma, 2 Binod K. Kanaujia, 3 Shekhar Rudra, 2 Ritu Raj Mishra, 2 and G.P. Pandey 4 1 Department of Electronics Engineering, Ambedkar Polytechnic, Delhi, India 2 Department of Electronics and Communication Engineering, Ambedkar Institute of Advanced Communication Technologies & Research, Delhi, India 3 ECE Department, M.J.P. Rohilkhand University, Bareilly, Uttar Pradesh, India; Corresponding author: bkkanaujia@yahoo.co.in 4 Department of Electronics and Communication Engineering, MAIT, Delhi, India Received 1 August 2012 ABSTRACT: In this paper, a novel orthogonal slit cut stacked circular patch antenna (SC-SCPA) is proposed for multi band operations. The antenna structure is investigated by cutting two pair of orthogonal slits on the upper patch whose effects are studied in terms of the return loss, input impedance, gain, directivity, and radiation pattern. Multiple resonances are observed that too at lower frequency signifying the compactness and multiband nature of the proposed antenna. The antenna is resonating at four operating frequencies 7.4, 9.0, 9.4, and 10.8 GHz, and 27% reduction in size is achieved by slit cut stacked patch antenna. The proposed theory which is verified by simulation and theoretical results is in good agreement with the simulated results obtained by Ansoft’s HFSS. The antenna is working in X-band from 7 to 12 GHz and applications pertaining to this regime are also discussed herein. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:873–882, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27416 Key words: multiband; orthogonal; stacked circular patch antenna (SCPA); slit cut stacked circular patch antenna (SC-SCPA); wideband 1. INTRODUCTION The microstrip patch antennas have been the consistent focus of research among the researchers since they came into exis- tence in 1970s. On the other side, features like low profile, inexpensive to manufacture, and compatible with monolithic microwave integrated circuits design have made microstrip antenna considerably interesting. Although their merits are ever superseded the demerits, a major demerit is limitation in bandwidth. The input impedance of a microstrip antenna depends on its geometrical shape, dimensions, and the fed type. Hence, input impedance of the antenna is a very impor- tant parameter which controls the radiated power and the im- pedance bandwidth. Numbers of methods have been suggested to enhance the bandwidth as in [1] along with several types of feeding methods [2]. Among them, most of the times, due to its robust nature, coaxial feeding technique is employed. The foremost method of increasing the bandwidth is to sim- ply increase the thickness of the dielectric substrate between the patch and ground plane. This may be done by including the air gap between ground plane and substrate [3]. However, this method cannot be extended too far without loss of low profile characteristics of the antenna with the excitation of undesirable higher order modes with minor increase in band- width is reported by such structures. Instead apart from many other structures, the stacked patch antennas (SPA) have been suggested [4–6]. In such structures, a parasitic patch stacked over the fed or driven patch and resulting in dual band char- acteristics. Dual-band antennas, however, may provide an al- ternative to larger bandwidth by facilitating two services in same antenna using different techniques as suggested [6, 7]. Such services are needed to operate at separate transmit- receive bands. The behavior of the antenna characteristics for the range of the intermediate frequencies may be of little or no concern. For this purpose, Long and Walton [6] designed and proposed dual-frequency antenna by stacking slightly dif- ferent sized circular discs [8]. Modern communication sys- tems and remote sensing (GPS, vehicular, etc.) often require compact antennas. Apart from compactness, operation at two or more bands is also a desired feature. Multiband or wide- band antennas are needed for multiservice systems when the lack of space is a determinant constraint or when multiple antenna installations are to be avoided [9–11]. Over the years, several techniques have been reported for dual band and mul- tiband antenna design. One of the widely accepted techniques to design a dual band/multiband/wideband antenna is loading the radiating patch with a slot, which when appropriately designed not only lower the fundamental resonant frequency of the antenna but also lead to a dual/wide band operation. The resonant frequency of the antenna is lowered by the meandering of the excited surface current paths in the slotted radiating patch. The meandering of the surface current paths can be achieved by loading several meandering slits at the boundary of a circular patch [12]. In this paper, a slit cut stacked circular patch antenna (SC- SCPA) for multiband operations is proposed. The antenna struc- ture is investigated by cutting two pair of slits on the upper radi- ating patch of antenna. The proposed antenna is theoretically an- alyzed on the basis of the extended cavity model and verified by simulation on the Ansoft’s HFSS. Upper patch is working as driven element with two pair of slit-cut while the lower patch is working as parasitic element. Although increased weight and thickness may present few limitations, still a level of compact- ness for multiband operations is achieved through the proposed antenna structure with the slit cut configuration. 2. THEORETICAL CONSIDERATIONS The structure of stacked circular patch antenna and its equiva- lent circuit are presented in the Figure 1. Both upper and lower patches are aligned with their center. The lower patch with ra- dius a 1 is supported by a substrate of dielectric constant e r1 and the upper one with radius a 2 placed on substrate of dielectric constant e r2 . The thickness of the lower substrate layer is h 1 and that of the upper substrate is h 2 . The heights h 1 and h 2 both are 0.32 mm such that the total height h ¼ h 1 þ h 2 ¼ 0.64 mm. The dielectric constants are e r1 ¼ e r2 ¼ 2.32 (Rogers RT/duroid 5870 TM ). The circular patch situated on the lower substrate has the radius of 6 mm while the upper patch is 5.4 mm in radius. The inner conductor of the coaxial feed passes through a clear- ance hole in the lower parasitic patch and is electrically con- nected to the upper driven patch. The lower patch is therefore coupled only through the fringing field. The two patches are aligned accurately so that the overall structure can be viewed as two coupled circular cavities. The cavity model developed for the single circular patch antenna [13] can now be extended for the stacked geometry. Figure 2 presents a 3D view of antenna structure drawn on the Ansoft’s HFSS for simulation of antenna. The numerical analysis of antenna is divided in four subparts. First, lower cavity has been analyzed with superstrate, neglect- ing the effect of upper patch. Second part describes design of upper cavity assuming lower patch as ground plane. Third, DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 4, April 2013 873